Must be our survival instinct. Or our aversion to pain. Or our ability to empathize with those who are suffering.
Does it mean that you make people to sit comfortably in an Air conditioned close room or in a car or birds/animals in cages in place of sitting them under a tree with cool & open air or devoid of walking or a nest/cave?
That wasn't the question. Are you advocating that no medical treatments be used on any illnesses?
Natural & social angles can be different, sometimes just opposite.
What natural systems? We survived by taming animals and plants, and by killing whatever else stared at us funny.
What in our lifestyle is "unnatural"? Which part of our lifestyle didn't come 100% from nature? Which piece of technology did we manage to sprout full grown without using materials from nature?
Taking a fruit in its natural form can be natural but taking it in some processed form can be unnatural. Alike all other foods. Burning woods for cooking food can be natural but microwave ovens, gas cooking, electric cooking can be unnatural. Walking or traveling on animals can be natural wheras traveling by car, aeroplanes..can be unnatural. A cave, a nest, a tree shelter, a cottage made from items in their natural forms, a jungle, a bath under waterfall..is natural whereas modern concrete jungles, shadows, bath in bathroom under shower..can be unnatural. Cloths made from cotton, natural fibers are natural but from synthetic fibers are unnatural. Alike it you can compare million of things OR can search google for natural & unnatural things. Whatever is new to us of which we do not having inherant sense of its right or wrong or whatever to which we are not habituated and adapted to, can be unnatural--as most modern things. There is a harmony or balance of all things in nature. Any deviation from this harmony can be taken as 'nature's imbalance' somewhat alike homeostatis. 3 apple, 3 pears & 3 lemons taken 1 each by three person can be a balance whereas each take all three of each can be said as imbalance....
Many or most people do enjoy going into the nature from cities.
You think diseases don't pass from one animal to another, when living in "nature"?
You are taking it differently. I meant we advocate killing of other species if posing them danger to humans but save the humans in similar situations(AIDS)--so selfishness.
You think animal populations in nature never suffered overpopulation?
Yes they can but they are then balanced, we may not by out interferances.
In nature everyone eats everyone else. I'd call that "interfering." And again, do you advocate eliminating all medical treatments, and all social assistance programs and charitable organizations?
Yes but to certain limit on "give & take' or 'live & let live' rules not "Let us only live" rule. Although "might is right" "Survival of fittest" is also said.

Social/unnatural & natural angles, self & whole considerations are different--may be bit opposite. What you prefer is your choice.